The motor that came with our recently-acquired Monotype Type and Rule Caster was fitted with 2″ a pulley suitable for a flat drive belt to run the caster. Such pulleys are shaped with a bit of a crown, that is, the pulley is a bit larger in diameter near the center of its length and tapers off a bit towards each end. This crown keeps the drive belt properly centered with no need for additional guides.
This particular pulley was, however, quite worn and the belt would not run on it properly, so it would need replacement. It was of an old style not seem much any more (not that flat belts themselves are used much in modern machinery either): a “paper pulley”. The main body of the pulley was just a tight stack of paper, more like boxboard (think of the stuff cereal boxes are made of), packed onto a hub and ends made of a single piece of metal. The metal is likely zinc or a zinc alloy, and was cast as one piece around the stacked cardboard.
One end of the pulley actually bears the markings “Browning Paper Pulleys” and “Maysville KY”, so “paper pulley” is indeed the correct name for these. The Browning company still exists in Maysville, but apparently they stopped making paper pulleys around 1977.
I pulled out most of the paper to see what else was inside. Because the pulley was cast onto the paper, it is actually difficult to remove all the paper cleanly, and much of it is left bonded to the metal in the hub:
One of the flanges has two holes in it, about ¼″ diameter, 45 degrees either side of the setscrew, and these holes continued into the stack of paper. The holes appear to have been drilled after the hub was cast around the paper. In the bottom of the holes there were two filler slugs that appeared to be the same metal as the hub, positioned about halfway lengthwise, and the rest of the holes were filled with cork. I’m not sure what purpose these serve, maybe this is how the pulley was balanced.
I’m not entirely sure how this would have been made. The layers of the paper core would probably be die-cut with a hole in the center to form the hub and a boss for the setscrew, but I don’t understand how they could be held tightly stacked while the hub was cast. There is no evidence of any sort of glue holding them together. It is possible, even likely, that the paper layers started off larger than the final diameter of the pulley, so the stack could have been held and lightly compressed by its edges. This would not, however, allow for much compression because the hub area of the stack would still bulge. Another possibility is that the paper was pressed hard in advance, and before it had a chance to rebound completely, the casting was done, followed by exposure to perhaps steam to soften the paper and allow it to puff up again to get everything tight.
Such pulleys now seem to be pretty much unobtanium, so I’m thinking of making myself a replacement. I’d make the hub and one flange as a single piece, the other flange as another piece, and use four bolts to pull the flanges together and compress the paper. The bolts will also transfer the torque from the flanges to the paper, and ideally the loose flange will be somehow keyed to the hub. Perhaps I can just weld it once the stack is tight.
Actually, McMaster-Carr appears to have a suitable replacement pulley for about $100, so I may just order that rather than taking on yet another side quest.
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